We report a comprehensive discussion of quantum interference effects due to the finite structure of excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. Anomalous features that appear in the experiments are analyzed according to theoretical models that describe the modulation of the interference pattern by temperature and built-in electric fields.PACS numbers: 71.35.Ji, 73.21.La, 78.20.Ls, 78.67.Hc The nanoscale ring structures, or quantum rings (QRs), have attracted the interest of the scientific community due to their unique rotational symmetry and the possibility to verify quantum mechanical phenomena.[1, 2, 3] Among these, the study of Aharonov-Bohm (AB)-like effects has gained a significant impetus, [4,5,6] and these efforts have gone beyond the original discussion of the AB interpretation on the nature of electromagnetic potentials and their role in quantum mechanics. [7] It is reasonable to say that the study of coherent interference occurring in transport properties of nanoscopic QRs, as proposed in Ref. 7 encounters, at the moment, serious scale limitations which has encouraged the search for optical implications associated to AB-effects.These endeavors applied to nanoscopic QRs do not strictly meet the original conditions for the ABconfiguration since the carriers are confined within regions with finite values of magnetic field. However, we still consider an observed effect as of AB-type if it can be explained assuming that the magnetic field is ideally concentrated in the middle of the QRs, i. e., when such effect comes essentially from potential vector-mediated quantum interference. As also considered in Ref. 8, in stationary systems this interference is generally reflected in a boundary condition and it is not as explicit as in the famous picture of an AB scattering situation.In this work we consider AB-interference in excitonic states as proposed theoretically in Refs. 9, 10, 12. Instead of looking only at the oscillatory dependence on magnetic flux of the electron-hole (e − h) recombination energy during photo-luminescence (PL), we also consider the excitonic oscillator strength whose oscillatory behavior reflects directly the changes in the exciton wavefunction as the magnetic flux increases. A similar experimental work was reported in Ref. 6 for type-II QRs, however, here we study type-I systems where both electron and hole move in the ring so that the correlation between them is crucial to the oscillatory behavior found in the PL integrated intensity. The samples studied here were grown using a RIBER 32P solid-source molecular beam epitaxy chamber and the QRs were grown using the following procedure. A 0.5 µm GaAs buffer layer was grown on semi-insulating (100) GaAs substrates at 580• C, after oxide desorption. Then, it was followed by 2.2 ML of InAs and the formation of quantum dots (QDs) at 520• C. The dots were obtained using the Stranski-Krastanov growth mode. Cycles of 0.14 ML of InAs plus a 2 s interruption under As 2 flux were r...
We compare InAlAs/GaAs and InGaAs/GaAs strained-layer superlattices (SLSs) as dislocation filter layers for 1.3-μm InAs/GaAs quantum-dot laser structures directly grown on Si substrates. InAlAs/GaAs SLSs are found to be more effective than InGaAs/GaAs SLSs in blocking the propagation of threading dislocations generated at the interface between the GaAs buffer layer and the Si substrate. Room-temperature lasing at ~1.27 μm with a threshold current density of 194 A/cm(2) and output power of ~77 mW has been demonstrated for broad-area lasers grown on Si substrates using InAlAs/GaAs dislocation filter layers.
Normal incident photodetection at mid infrared spectral region is achieved using the intersublevel transitions from strain-free GaAs quantum dot pairs in Al(0.3)Ga(0.7)As matrix. The GaAs quantum dot pairs are fabricated by high temperature droplet epitaxy, through which zero strain quantum dot pairs are obtained from lattice matched materials. Photoluminescence, photoluminescence excitation optical spectroscopy, and visible-near-infrared photoconductivity measurement are carried out to study the electronic structure of the photodetector. Due to the intersublevel transitions from GaAs quantum dot pairs, a broadband photoresponse spectrum is observed from 3 to 8 microm with a full width at half-maximum of approximately 2.0 microm.
Building optoelectronic devices on a Si platform has been the engine behind the development of Si photonics. In particular, the integration of optical interconnects onto Si substrates allows the fabrication of complex optoelectronic circuits, potentially enabling chip-to-chip and system-to-system optical communications at greatly reduced cost and size relative to hybrid solutions. Although significant effort has been devoted to Si light generation and modulation technologies, efficient and electrically pumped Si light emitters have yet to be demonstrated. In contrast, III–V semiconductor devices offer high efficiency as optical sources. Monolithic integration of III–V on the Si platform would thus be an effective approach for realizing Si-based light sources. Here, we describe the first superluminescent light-emitting diode (SLD) monolithically grown on Si substrates. The fabricated two-section InAs/GaAs quantum-dot (QD) SLD produces a close-to-Gaussian emission spectrum of 114 nm centered at ∼1255 nm wavelength, with a maximum output power of 2.6 mW at room temperature. This work complements our previous demonstration of an InAs/GaAs QD laser directly grown on a Si platform and paves the way for future monolithic integration of III–V light sources required for Si photonics.
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